1. Field of the Invention
The invention concerns the necessary physical and chemical composition and construction of a transmission phantom for total performance assessments in scintillation camera imaging. In particular, the transmission phantom of this invention concerns the simulation of complex distribution patterns of radionuclides, for example, as obtained in bone scintigraphy. When placed on top of a uniform source of radioactivity, the phantom creates a photon intensity distribution directed towards the detector that is equivalent to that which is observed in a patient study. The design technique also enables simulations of studies where there are complex distributions of radioactivity within the human body in front of the camera, e.g. in bone scintigraphy. The invention further concerns a method for mass production of this phantom.
2. Description of the Related Art
A scintillation camera (gamma camera) is currently used in nuclear medicine to acquire images of photon-emitting radionuclides distributed within the patients body following an intravenous injection, after breathing a radioactive gas or after an oral intake of radionuclides. Such cameras are used in most larger hospitals. In Norway they are used in 23 hospital laboratories. Artificially produced radionuclides are used, and they are required to be photon-emitters and have relative short half lives.
These cameras perform an indirect imaging, in the sense that the detection process is based on electronic circuits that must be correctly adjusted if artificial structures (artefacts), not related to the distribution of radionuclides, shall be avoided. Most laboratories therefore posess simple constructions made of lead to be used together with radioactive sources for monitoring camera quality.
Devices for quality control of scintillation cameras are previously described. U.S. Pat. No. 4,408,124 comprises a lead plate, impervious to gamma rays, with an orthogonal array of apertures sandwiched between two rectangular sheets of lucite, while U.S. Pat. No. 4,419,577 comprises a radiation transparent, closed, planar body member with internal mercury-filled communication passages that define a calibrated radiation opaque test pattern. These devices are suitable for testing scintillation camera performance (uniformity, linearity, intrinsic resolution). They do, however, not simulate the complex distribution of radioactivity in a patient since, 1) the gamma impervious lead plate in U.S. Pat. No. 4,408,124 is of constant thickness, and the apertures are of uniform size; and 2) the low attenuating body member in U.S. Pat. No. 4,419,577 is planar, of constant thickness, and the mercury bars all have uniform thickness and attenuation, and thus represent only two levels of transmission (mercury bar/lucite, lead plate/apertures).
From the literature, hollow containers, filled with radioactive solutions are known, and in which objects of different materials may be inserted to displace the radioactive solution and thereby simulate uptake defects. Also, simple transmission phantoms have been built as combinations of several layers of absorptive material (e.g. copper). By the use of a uniform source behind such a phantom, a transmitted photon intensity distribution resembles that obtained in a patient study. None of these constructions re suited for simulations of more complex distributions of radioactivity in the patient, such as when the radionuclides are accumulated in bone tissues.